Our first challenge was to find ways to convert our daily activities into pounds of CO2. We wanted to track our progress as we went, to change our habits if necessary.

PJ volunteered to read our electric meter each morning and to check the odometer on our Mazda Miata. While she was doing that, I wrote down the mileage from our Honda CR-V and pushed my way through the shrubs to read the natural gas meter. We diligently recorded everything on a chart taped to one of our kitchen cabinets. A gallon of gasoline, we learned, adds a whopping 19.6 pounds of CO2 to the atmosphere, a big chunk of our daily allowance. A kilowatt-hour (kWh) of electricity in the U.S. produces 1.5 pounds of CO2. Every 100 cubic feet of natural gas emits 12 pounds of CO2.

To get a rough idea of our current carbon footprint, I plugged numbers from recent utility bills into several calculators on websites. Each asked for slightly different information, and each came up with a different result. None was flattering. The Environmental Protection Agency (EPA) website figured our annual CO2 emissions at 54,273 pounds, 30 percent higher than the average American family with two people; the main culprit was the energy we were using to heat and cool our house. Evidently, we had further to go than I thought.

I began our campaign by grabbing a flashlight and heading down to the basement. For most families, the water heater alone consumes 12 percent of their house's energy. My plan was to turn down the heater's thermostat to 120�F, as experts recommend. But taking a close look at our tank, I saw only "hot" and "warm" settings, no degrees. Not knowing what that meant exactly, I twisted the dial to warm and hoped for the best. (The water turned out to be a little cool, and I had to adjust it later.)

When PJ drove off in the CR-V to pick up a friend for church, I hauled out gear to cut the grass: electric lawn mower, electric edger, electric leaf blower. Then it dawned on me: All this power-sucking equipment was going to cost us in CO2 emissions. So I stuffed everything back into the garage, hopped in the Miata, and buzzed down the street to Home Depot to price out an old-fashioned push reel mower.

The store didn't have one, so I drove a few miles more to Lawn & Leisure, an outfit that specializes in lawn mowers. They were out too, though they had plenty of big riding mowers on display. (The average gasoline-powered push mower, I'd learned, puts out as much pollution per hour as eleven cars—a riding mower as much as 34 cars.) My next stop was Wal-Mart, where I found another empty spot on the rack. I finally tried Sears, which had one manual mower left, the display model.